Delhi’s air quality could dip over the weekend after improving over past 48 hours

According to government agencies, pollution levels in Delhi could rise gradually over the weekend as the wind speed could drop from Saturday. However, the AQI is unlikely to slide back to the “very poor” levels.

Pollution levels in Delhi dropped significantly and the Air Quality Index (AQI), as recorded by the Central Pollution Control Board (CPCB), improved by nearly 200 notches over the past two days, thanks to rain and high-velocity winds that helped disperse pollutants.

On Thursday, November 15, 2018, the air quality of the Capital improved to 217, in the ‘poor’ category, from ‘very poor’ a day earlier. (Burhaan Kinu/HT PHOTO)

Government agencies, however, have forecasted that the pollution levels could rise gradually over the weekend as the wind speed could drop from Saturday. However, the AQI is unlikely to slide back to the “very poor” levels.

An AQI between 0 and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor” and that between 401 and 500 is categorised as “severe”.

The AQI, which was recorded at 409 on Tuesday, in the “severe” category, improved to 312 on Wednesday, to the “very poor” category. On Thursday, it improved to 217, to the “poor” category.

“The air quality has improved significantly. There was rain for two consecutive nights, the wind speed has picked up and the mixing height — the height to which pollutants can rise and disperse — has also increased. The ventilation index — which determines how fast pollutants can disperse — has also increased, said a scientist from the Indian Institute of Tropical Meteorology, one of the two pollution forecasting agencies in Delhi.

Delhi needs a minimum ventilation index of 6,000m2/second and wind speed of at least 10 km/hour for pollutants to disperse. On Thursday, the wind speed increased to 10km/hr and the ventilation index was around 15,000m2/second. This helped clear pollutants that had accumulated over the past few days owing to unfavourable weather conditions.

“The wind speed is expected to increase further on Friday, facilitating more dispersal of pollutants. The AQI will, consequently, improve further,” an IITM scientist said.

From Saturday, however, the wind speed is likely to drop as a result of which pollution could start accumulating again.

“We are expecting the pollution to rise marginally from Saturday, as clam winds would be unable to disperse the pollutants. Pollution from local emissions would once again accumulate,” a CPCB scientist said.